Arthroplasty is surgery to relieve pain and restore range of motion by realigning or reconstructing a joint. Typical arthroplastic options include joint resection, interpositional reconstruction, and total joint replacement. Joint resection involves removing a portion of a bone from a joint to create a gap between the bone and the corresponding socket, thereby improving the range of motion. Scar tissue eventually fills the gap. Pain may be relieved and motion restored, but the joint is typically less stable. Interpositional reconstruction reshapes the joint and adds a prosthetic disk between the bones forming the joint. The prosthesis can be made of plastic and metal or from body tissue such as fascia and skin. If the joint does not respond to the more conservative treatments (which may include medication, weight loss, activity restriction, and/or use of walking aids such as a cane), joint replacement is often considered appropriate. Joint replacement (i.e., total joint arthroplasty) is the surgical replacement of a joint with a prosthesis. Many joint replacements are needed because arthritis has caused the joint to stiffen and become painful to the point where normal daily activities are no longer possible. Arthroplasty, especially joint replacement, is becoming an increasingly prevalent treatment. For example, it has been reported that more than 170,000 hip replacements and more than 200,000 knee replacements are performed in the United States each year. 1 See Gale Encyclopedia of Medicine, Gale Research (1999), found at http://www.findarticles.com/cf_dls/g2601/0007/2601/000783/p1/article.jhtml?term=.
A conventional hip prosthesis includes an artificial socket and a femoral stem. The artificial socket is typically made of metal coated and polyethylene (a plastic) to reduce friction. The femoral stem has a ball at one end and an elongated post or spike at the other. In a relatively simple hip replacement operation, the surgeon makes an incision in the area of the distal femur and then pulls the distal femur away from the acetabulum (socket of the hip bone). Next, the surgeon inserts the artificial socket into the acetabulum. The surgeon cuts and shapes the distal femur, inserts the post of the femoral stem into the medullary canal of the distal femur, and fits the ball of the stem into the artificial socket. The surgeon secures the artificial socket and the post of the stem within the acetabulum and the medullary canal, respectively, with an acrylic polymer (a synthetic cement). Alternatively, the artificial socket and the post may be designed for fixation by natural bone in-growth.
However, not all hip replacements are so simple. Impaction grafting is increasingly incorporated in cases that are complicated by substantial bone loss within the femur. Impaction grafting is a technique in which the surgeon uses impaction grafting tamps to impact morselized allograft (a replacement material typically made from bone chips, among other things) into the medullary canal of the femur. The allograft creates a new canal for receiving the femoral stem.
Conventional impaction grafting approaches include progressively impacting the subject bone cavity with allograft to ensure a high overall finished graft integrity. But properly aligning and otherwise manipulating the differently sized and shaped tamps needed for progressive impaction grafting has been challenging.